fbbd9655e5
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
140 lines
3.9 KiB
Groff
140 lines
3.9 KiB
Groff
.\" Copyright (c) 1980, 1991 Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" from: @(#)fork.2 6.5 (Berkeley) 3/10/91
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.\" $FreeBSD$
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.\"
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.Dd October 14, 2006
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.Dt I386_GET_LDT 2
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.Os
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.Sh NAME
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.Nm i386_get_ldt ,
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.Nm i386_set_ldt
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.Nd manage i386 per-process Local Descriptor Table entries
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In machine/segments.h
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.In machine/sysarch.h
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.Ft int
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.Fn i386_get_ldt "int start_sel" "union descriptor *descs" "int num_sels"
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.Ft int
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.Fn i386_set_ldt "int start_sel" "union descriptor *descs" "int num_sels"
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.Sh DESCRIPTION
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The
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.Fn i386_get_ldt
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system call
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returns a list of the i386 descriptors in the current process'
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LDT.
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The
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.Fn i386_set_ldt
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system call
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sets a list of i386 descriptors in the current process'
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LDT.
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For both routines,
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.Fa start_sel
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specifies the index of the selector in the LDT at which to begin and
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.Fa descs
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points to an array of
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.Fa num_sels
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descriptors to be set or returned.
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.Pp
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Each entry in the
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.Fa descs
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array can be either a segment_descriptor or gate_descriptor and are defined in
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.In i386/segments.h .
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These structures are defined by the architecture
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as disjoint bit-fields, so care must be taken in constructing them.
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.Pp
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If
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.Fa start_sel
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is
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.Em LDT_AUTO_ALLOC ,
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.Fa num_sels
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is 1 and the descriptor pointed to by
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.Fa descs
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is legal, then
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.Fn i386_set_ldt
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will allocate a descriptor and return its
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selector number.
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.Pp
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If
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.Fa num_descs
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is 1,
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.Fa start_sels
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is valid, and
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.Fa descs
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is NULL, then
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.Fn i386_set_ldt
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will free that descriptor
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(making it available to be reallocated again later).
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.Pp
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If
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.Fa num_descs
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is 0,
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.Fa start_sels
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is 0 and
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.Fa descs
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is NULL then, as a special case,
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.Fn i386_set_ldt
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will free all descriptors.
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.Sh RETURN VALUES
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Upon successful completion,
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.Fn i386_get_ldt
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returns the number of descriptors currently in the LDT.
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The
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.Fn i386_set_ldt
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system call
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returns the first selector set on success.
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If the kernel allocated a descriptor in the LDT,
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the allocated index is returned.
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Otherwise, a value of -1 is returned and the global
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variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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The
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.Fn i386_get_ldt
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and
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.Fn i386_set_ldt
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system calls
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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An inappropriate value was used for
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.Fa start_sel
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or
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.Fa num_sels .
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.It Bq Er EACCES
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The caller attempted to use a descriptor that would
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circumvent protection or cause a failure.
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.El
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.Sh SEE ALSO
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i386 Microprocessor Programmer's Reference Manual, Intel
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.Sh WARNING
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You can really hose your process using this.
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